Method for making an avalanche photodiode

Abstract

An avalanche photodiode includes a region of second conductivity type extending a distance into a substrate and a region of first conductivity type extending a further distance into the substrate of first conductivity type with a P-N junction therebetween. The invention is a method for fabricating an avalanche photodiode having a specified breakdown voltage. The method includes the step of measuring the concentration of the first type conductivity modifiers and removing a portion of the surface of the substrate prior to forming the region of second conductivity type. This method provides control of the concentration of the first type conductivity modifiers at the P-N junction and thereby controls the breakdown voltage.

I claim: 
     
       1. A method of making an avalanche photodiode comprising the steps of: embedding first type conductivity modifiers into a semiconductor body have a first conductivity type through a portion of a surface thereof wherein the concentration of first type conductivity modifiers is greater than the concentration of first type conductivity modifiers originally in said body;   measuring the concentration of said embedded first type conductivity modifiers;   removing material from said portion of said surface corresponding to the variation in the measured local concentration of said embedded first type conductivity modifiers; and   embedding second type conductivity modifiers having the opposite conductivity type to said first type conductivity modifiers into said body through said portion of said first surface in a concentration sufficient to convert a region of said body adjacent to said portion of said surface to said second conductivity type.   
     
     
       2. The method of claim 1 wherein said first type conductivity modifiers are diffused a distance into said body prior to the step of measuring the concentration of said first type conductivity modifiers. 
     
     
       3. The method of claim 2 wherein said portion of said surface adjacent the region containing said first type conductivity modifiers is uniformly etched to remove material from said body. 
     
     
       4. The method of claim 2 wherein the step of embedding said first type conductivity modifiers comprises ion implanting said first type conductivity modifiers into said body. 
     
     
       5. The method of claim 4 wherein the body is π-type conductivity silicon and the embedded first type conductivity modifier is boron. 
     
     
       6. The method of claim 2 wherein said portion of said surface adjacent the region containing said first type conductivity modifiers is selectively etched to remove material from said body corresponding to the variation in first type conductivity modifier concentration. 
     
     
       7. A method of making an avalanche photodiode comprising the steps of: embedding conductivity modifiers of a first conductivity type into a plurality of spaced apart regions of a wafer of semiconductor material, said regions extending a distance into said wafer from a first surface thereof, wherein the concentration of embedded first type conductivity modifiers is greater than the concentration of first type conductivity modifiers originally in said body;   measuring the concentration of said embedded conductivity modifiers in each of said regions;   masking said first surface adjacent a first fraction of said regions having a measured concentration less than a particular value, thereby forming first masked regions;   selectively removing material from said first surface adjacent the unmasked regions; and   embedding second type conductivity modifiers having the opposite conductivity type to said first conductivity type modifiers into each of said plurality of regions sufficient to convert a portion thereof adjacent said first surface to second conductivity type.